1. Field of the Invention
This invention relates to compositions useful for generating foam and more particularly to compositions for use in foaming agents during, for example, the manufacture of gypsum board or concrete, and to processes for using such compositions.
2. Statement of Related Art
Generally, gypsum board consists of a core of set gypsum surfaced with paper or other fibrous material suitable to receive a coating such as paint. It is common to manufacture gypsum board by placing an aqueous core slurry ("slurry") composed predominantly of calcined gypsum between two sheets of paper thereby forming a board. The resultant core is allowed to set or harden by rehydration of the calcined gypsum, usually followed by heating the gypsum board in a dryer so as to drive away any excess water.
It is common practice to introduce air bubbles into the slurry to reduce its density and to reduce the amount of water necessary to produce a workable slurry. This is normally achieved by the addition of a foaming agent, comprised of an active ingredient along with other additives, during the formation of the slurry or by adding externally-generated foam to the slurry. The externally-generated foam is normally produced by incorporating air or other gas into an aqueous solution of a foaming agent; the resulting mixture is then mixed with the slurry.
Foaming agents generally contain as active ingredients one or more salts of alkyl ether sulfates. Known salts of alkyl ether sulfates employed in foaming agents, such as those disclosed in Cukier U.S. Pat. No. 4,156,615, Green et al. U.S. Pat. Nos. 4,618,370, 4,676,835 and 4,678,515, and UK published patent application GB 2 196 334 have the general formula I: EQU CH.sub.3 (CH.sub.2).sub..times. CH.sub.2 (OCH.sub.2 CH.sub.2).sub.y OSO.sub.3.sup.- M.sup.+ (I),
where x and y represent integers which may be the same or different and may have non-integral average values in any practical sample size because of the method of synthesis, and M.sup.+ represents either sodium or ammonium ion.
In a practical mixture of such foaming agents as commercially used, the distribution of molecules having particular numbers of ethoxy units, as represented by y in formula I, can be represented in the form of a generally bell-shaped curve in which the number or fraction of molecules containing a particular number of ethoxy unit is plotted versus the number of such ethoxy units, starting at y=0 (representing unethoxylated starting material). The broader the curve, the more evenly distributed are values of y. The narrower the curve, the more narrowly distributed are values of y. Methods are available for separating compounds of formula I having specified values of x and y from compounds having other values of x and/or y, but these methods are tedious and expensive and are not believed to be used in industrial practice.
Accordingly, an object of this invention is to provide practicable compositions in which the individual molecules in the composition conform to formula I or a similar formula but the distribution of values of y in the mixture is more favorable for foaming than in the mixtures available heretofore.